Foamed cementitious materials are desirable as building and construction materials because of their light weight and conformability.
In U.S. Pat. No. 2,432,971, Ruthman et al. taught the use of a methyl cellulose gel-like solution, activatible by heating, for preventing structural collapse or migration of components in foams whose constituents were initially water-soluble or water-dispersible. Such constituents include foaming materials except those which render the methyl cellulose ineffective. Suitable foaming agents include saponin containing materials, such as soap bark, soap weed, yucca root, pure saponin, etc. Foaming materials considered unsuitable include sodium and potassium salts of fatty acids (see e.g., column 6, lines 1-17). A number of fiber materials can be mixed into the foam, including cellulose fibers in the form of dried ground paper.
In U.S. Pat. No. 3,867,159, Dilnot disclosed the use of aqueous slurries, comprising finely ground calcareous and siliceous materials, and pre-soaked cellulose fibers to generate light weight materials. The foam is formed in advance of its mixture with the aqueous slurry, so that the bubbles do not substantially coalesce or break down when subsequently mixed into the slurry. Heating the foamed slurry by autoclave produces a rigid matrix having macroscopic spherical voids.
In U.S. Pat. No. 3,758,319 and No. 3,867,159, Ergene disclosed cellular structures made by admixing water and cement under conditions sufficient to produce a high degree of hydration of the cement, followed by introducing foam that has been formed under pressure using water, air, foaming agent (e.g., saponin, peptone, albumin, soap bark, water-soluble cellulose ester), and a chloride accelerator. The foam mixture and cement mixture are blended to a substantially homogeneous, foamed cement slurry, which is cast into a mold and cured (e.g., environmental steam or autoclave) to form a lightweight cellular concrete structure.
In U.S. Pat. No. 3,963,507, Kuramoto et al. disclosed a porous construction material comprising a hydraulic material such as cement and a foaming agent comprising a water-soluble low-viscosity cellulose ether (e.g., 25-2000 centipoise), a water-soluble high-viscosity cellulose derivative (e.g., exceeding 2000 centipoise), and a PVOH foaming accelerator which was at least 75%, and more preferably at least 85%, saponified.
In U.S. Pat. No. 3,989,534, Plunguian disclosed cementitious materials comprising lightweight filler such as perlite, vermiculite, or hollow silicate spheres in combination with a surface active foaming agent and water-soluble organic film forming agents such as guar gum, pregelatinized starch, xanthan gum, and the like, which function as foam stabilizers. In U.S. Pat. No. 4,077,809, Plunguian explained a method wherein the cement and light weight fillers and film forming agents could be combined with pre-formed foams to create a foamed cementitious material useful for soundproofing and thermal insulation.
In U.S. Pat. No. 4,731,389, Christopher et al. (Aircrete) disclosed methods for making foams suitable for insulating cavities and structures. One example involved injecting air into an aqueous solution of PVOH and a dispersant, and then adding the resultant foam to an aqueous solution or suspension of magnesium oxide and barium metaborate and a dispersant. An objective of the inventors was to provide a foam-cement mixture wherein the foam maintained sufficient integrity to maintain its shape and volume until the inter-mixed cement hardened to fix the composition in place (col. 1, II. 37-42); and this was accomplished by mixing PVOH (polyvinyl alcohol) from the first component with barium metaborate in the second component to initiate and to accelerate the setting of the foam, while providing integrity for supporting the cement as it hardened in place (See col. 3, II. 37; See also col. 4, II. 12-20).
In U.S. Pat. No. 5,110,839, Chao disclosed a foamed composition comprising (a) about 100 parts by weight of a hydraulic substance such as Portland cement, gypsum, or Plaster of Paris; and (b) about 25 to less than about 70 parts by weight water and about 0.01 to about 10 parts by weight of a polymeric foam stabilizer having a weight average molecular weight of from about 1,000 to about 20,000 and comprising a C1-C12 alkyl carboxylic acid polymer. This composition could be formed by mixing a homogeneously foamed mixture of water and polymeric stabilizer, and homogeneous slurry comprising cement and polymeric foam stabilizer.
In U.S. Pat. No. 5,641,584, Anderson et al. disclosed insulation barrier materials having cement paste in combination with a rheology modifying agent (e.g., methylhydroxyethylcellulose) and a lightweight aggregate (e.g., perlite, vermiculite, hollow glass spheres, etc.) to lower the density of the insulation barrier and increase its insulation ability. A preferred method for making the insulation barrier materials includes the steps of (1) mixing a powdered hydraulic cement and water to form a cement paste; (2) combining a rheology-modifying agent (methylhydroxyethylcellulose) with cement paste such that the resultant cementitious mixture develops a more plastic rheology; (3) adding an aggregate material and/or entrained air to the cementitious mixture to impart desired lightweight properties; (4) adding a fibrous material (such as abaca, glass, plastic, or metal fiber) preferably having a high aspect (length to width) ratio to the cementitious mixture in order to increase toughness and strength; (5) molding the mixture into an insulation barrier of a predetermined shape; and (6) allowing the cementitious mixture to harden into the predetermined shape. It was desired to obtain insulation barriers that were “form stable” in less than ten minutes.
In U.S. Pat. No. 6,547,871 and No. 6,797,054, Chatterji et al. disclosed foamed well cement slurries which were comprised of hydraulic cement, sufficient water to form pumpable slurry, sufficient gas to generate foam, and hydrolyzed keratin for stabilizing the foam within the slurry.
In U.S. Pat. No. 6,780,230 and World Patent App. No. WO 03/060018, Hilton et al. disclosed formulations and methods for spray-applying cementitious fireproofing compositions onto a substrate. Pumpable cementitious slurry is formed and mixed with air, and then the slurry is subjected to mechanically created turbulence to generate gas bubbles and create a foam which is preferably stabilized by the presence of polyvinyl alcohol contained in the slurry. The slurry is pumped through hoses to a nozzle for spray application. However, prior to dispensing, a set accelerator is injected into the foam slurry which causes the foam to gel, which in turn improves the hangability of the foam on the substrate.
Thus, various foamed cementitious systems are known in the art for a variety of applications and uses in the building and construction industries.